负离子聚合制备环氧化八臂星形聚异戊二烯及其表征

Anionic Synthesis and Characterization of Epoxidized Eight-arm Star-shaped Polyisoprene

利用仲丁基锂引发异戊二烯进行高真空负离子聚合制备聚异戊二烯基锂活性链(PI-Li),再与八乙烯基多面体齐聚倍半硅氧烷(OVPOSS)在环己烷中发生加成反应,一步法制得八臂星形聚合物.利用分级沉淀去除稍过量的的线型聚异戊二烯以及低加成产物,即可得到纯的八臂星形聚异戊二烯(8PI-POSS).最后,通过甲酸/过氧化氢对8PI-POSS中的聚异戊二烯链进行部分氧化反应,获得环氧化八臂星形聚异戊二烯(8EPI-POSS).利用核磁共振波谱(~1H-,^(13)C-NMR)、凝胶渗透色谱(GPC)、傅里叶变换红外光谱(FTIR)和基质辅助激光解吸电离飞行时间质谱(MALDI-TOF MS)对聚合物的化学结构、分子量及分子量分布进行表征.实验结果表明,通过调节单体与引发剂的摩尔比,成功合成了不同聚合度的8PI-POSS和8EPI-POSS;并且通过改变氧化反应的温度和时间以及氧化试剂的用量,可以简易改变8EPI-POSS的环氧度.最后,通过热失重分析(TGA)测试了几种聚合物的热分解温度,结果显示,PI均聚物在200oC左右开始分解,而由于POSS的引入,8PI-POSS和8EPI-POSS在340oC左右才开始分解,并且与PI均聚物相比,在800oC还有大概3%的残留组分.

The synthesis of epoxidized star-shaped polymers by incorporation of living anionic polymerization with polyhedral oligomericsilsesquioxane（POSS） is seldom reported. In this study, the living（polyisopryl）lithium（PI-Li） is first synthesized in cyclohexane via high-vacuum living anionic polymerization using sec-butyllithium as the initiator and isoprene as the monomer. Subsequently, PI-Li is used to react with octavinyl polyhedral oligomericsilsesquioxane（OVPOSS） in cyclohexane to prepare an eight-arm star-shaped polyisoprene（8 PI-POSS） in one pot. Purified 8 PI-POSS is obtained after fractionation precipitation using cyclohexane/ethanol as solvent/nonsolvent, and characterized by nuclear magnetic resonance（~1 H-and ^（13） C-NMR）, gel permeation chromatography（GPC）, matrix-assisted laser desorption/ionization time-of-flight（MALDI-TOF） mass spectroscopy and Fourier transform infrared spectroscopy（FTIR）, respectively. Star-shaped polyisoprenes with different arm lengths are synthesized by changing the feed ratio of the monomer to the initiator. The compositions of the polymers are determined by comparison of integrals of characteristic signals from ~1 H-NMR spectra. GPC tests demonstrate that the eluent curves of the crude star-shaped polyisoprenes show an apparent shift to higher molecular weight compared with that of the base PI. The purified star-shaped polyisoprene（8 PI-POSS） by fractionation precipitation possesses symmetric peaks with relatively narrow polydispersity. MALDI-TOF MS analysis indicates that the observed molecular weight of base PI is in good agreement with the calculated value. In addition, there are two minor peaks with an interval of 16 Da in the MALDI-TOF MS spectrum, which may be attributed to the possible oxidation reaction during storage or MALDI-TOF MS test. Unfortunately, the MALDI-TOF MS spectra of 8 PI-POSS are not obtained probably due to their high molecular weights. Finally, the epoxidized star-shaped polyisoprene（8 EPI-POSS） is obtained by oxidation of 8 PI-POSS catalyzed by HCOOH/H_2O_2. The 8 EPI-POSS polymer is also characterized by 1 H-and 13 C-NMR, GPC and FTIR analyses, respectively. The characteristic signals found in ~1 H-and ^（13） C-NMR spectra, as well as in FTIR spectra confirm the formation of epoxy group in the 8 EPI-POSS. By changing the temperature and time of oxidation reaction, the star-shaped 8 EPI-POSS with different percentages of epoxidation（PE） are prepared. It is also found that the GPC eluent curve of 8 EPI-POSS change a little after the oxidation reaction. TGA tests show that the thermal decomposition temperature of 8 PI-POSS and 8 EPI-POSS are higher than that of the base PI. Moreover, it is also found that about 3% residue is left at about 800 oC, which maybe because of the incorporation of POSS segment in the star-shaped polymers. The epoxidized star-shaped polyisoprenes reported here may serve as an important intermediate in the preparation of highly branched polymers and as the novel tougheners for epoxy resins.